Evidence of five digits in embryonic horses and developmental stabilization of tetrapod digit number.

Previous work comparing the developmental mechanisms involved in digit reduction in horses with other mammals reported that horses have only a 'single digit', with two flanking metapodials identified as remnants of digit II and IV. Here we show that early Equus embryos go through a stage with five digit condensations, and that the flanking splint metapodials result from fusions of the two anterior digits I and II and the two posterior digits IV and V, in a striking parallel between ontogeny and phylogeny. Given that even this most extreme case of digit reduction exhibits primary pentadactyly, we re-examined the initial stages of digit condensation of all digit-reduced tetrapods where data are available and found that in all cases, five or four digits initiate (four with digit I missing). The persistent pentadactyl initiation in the horse and other digit-reduced modern taxa underscores a durable developmental stability at the initiation of digits. The digit evodevo model may help illuminate the biological circumstances under which organ systems become highly stabilized versus highly plastic.

Antimicrobial Activity of Ceftiofur and Penicillin With Gentamicin Against Escherichia coli and Streptococcus equi Subspecies zooepidemicus in an Ex Vivo Model of Equine Postpartum Uterine Disease.

The use of antimicrobials for the management of equine uterine disease is commonplace, with antibiotic selection generally based on empirical evidence or in vitro sensitivity results. However, the potential disconnect between these laboratory results and clinical efficacy in the mare raises concern for antibiotic failure and subsequent development of resistant organisms. In this work, we attempt to bridge this gap by using an ex vivo model of the equine postpartum uterus to quantitatively evaluate the antimicrobial activity of two commonly used antibiotic treatments in the mare (ceftiofur and penicillin with gentamicin). The activity of both of these treatments was evaluated in two different fluid environments (standard bacterial culture broth and equine postpartum uterine fluid) against clinical isolates of E. coli and S. zooepidemicus. Although treatment with ceftiofur was effective at reducing growth of S. zooepidemicus in equine postpartum uterine fluid, it did not reduce bacterial growth of E. coli. Treatment with procaine penicillin G with gentamicin achieved at least bacteriostatic activity against E. coli in both fluid types, and bactericidal activity against S. zooepidemicus in both fluid types. The intrauterine infusion of procaine penicillin G with gentamicin in cases of postpartum uterine disease caused by E. coli or S. zooepidemicus is supported by the results of this work.

Pharmacokinetics of Intrarectal Altrenogest in Horses.

Hospitalized pregnant mares being held nil per os (PO) because of medical or surgical events present a dilemma for pregnancy maintenance therapy, which commonly includes oral altrenogest. Rectal administration of medications is a recognized route for achieving systemic concentrations, but there are no data on the pharmacokinetics of rectal altrenogest administration in horses. The purpose of this study was to determine the pharmacokinetics of altrenogest following PO or per rectum (PR) administration in mares. Using a randomized two-way crossover study design, six horses received altrenogest (0.088 mg/kg; PO or PR q 24 hours for 5 days), with a 7-day washout period, and the concentrations of altrenogest were determined by an ultrahigh performance liquid chromatography with tandem mass spectrometry. Plasma concentrations persisted above presumed therapeutic concentrations for a mean of 36 hours (range 24-72 hours) and 5.5 hours (range 3-8 hours) for PO and PR administration, respectively. The calculated half-life (T ½) of PO administration (7.01 ± 3.13 hours) was correspondingly increased when compared to PR administration (2.82 ± 1.07 hours). Relative bioavailability of altrenogest following PR administration was only 5.47%. Altrenogest is rapidly absorbed following PR administration in the horse and reaches therapeutic concentrations, making this a viable method of treatment in NPO mares. The decreased bioavailability and shorter detection time suggest 0.088 mg/kg PR q 4-8 hours would be necessary to maintain therapeutic concentrations over a 24-hour period.

Collection and characterization of semen from Chilean rose tarantulas (Grammostola rosea).

OBJECTIVE: To establish a nonterminal semen collection method for use in captive Chilean rose tarantulas (Grammostola rosea) and to evaluate tools for investigating morphology and viability of spermatozoa. ANIMALS: 7 mature male Chilean rose tarantulas. PROCEDURES: Each tarantula was anesthetized in a 500-mL induction chamber containing a cotton ball infused with 2 mL of isoflurane. Semen collection was performed by applying direct pressure to the palpal bulbs (sperm storage organs) located on the distal segment of the palpal limbs. Morphology of spermatozoa was examined by light microscopy and transmission and scanning electron microscopy. Propidium iodide and a fluorescent membrane-permeant nucleic acid dye were used to evaluate cell viability. RESULTS: Semen was collected successfully from all 7 tarantulas. Microscopic examination of semen samples revealed coenospermia (spherical capsules [mean ± SD diameter, 10.3 ± 1.6 µm] containing many nonmotile sperm cells [mean number of sperm cells/capsule, 18.5 ± 3.8]). Individual spermatozoa were characterized by a spiral-shaped cell body (mean length, 16.7 ± 1.4 µm; mean anterior diameter, 1.5 ± 0.14 µm). Each spermatozoon had no apparent flagellar structure. The fluorescent stains identified some viable sperm cells in the semen samples. CONCLUSIONS AND CLINICAL RELEVANCE: The described technique allowed simple and repeatable collection of semen from Chilean rose tarantulas. Semen from this species was characterized by numerous spherical capsules containing many nonmotile spermatozoa in an apparently quiescent state. Fluorescent staining to distinguish live from dead spermatozoa appeared to be a useful tool for semen evaluation in this species.

Constraints on Mammalian forelimb development: insights from developmental disparity.

Tetrapod limb development has been studied extensively for decades, yet the strength and role of developmental constraints in this process remains unresolved. Mammals exhibit a particularly wide array of limb morphologies associated with various locomotion modes and behaviors, providing a useful system for identifying periods of developmental constraint and conserved developmental mechanisms or morphologies. In this study, landmark-based geometric morphometrics are used to investigate levels and patterns of morphological diversity (disparity) among the developing forelimbs of four mammals with diverse limb morphologies: mice, opossums, horses, and pigs. Results indicate that disparity among the forelimbs of these species slightly decreases or stays the same from the appearance of the limb ridge to the bud stage, and increases dramatically from the paddle through tissue regression stages. Heterochrony exhibited by the precocial opossum limb was not found to drive these patterns of morphological disparity, suggesting that the low disparity of the middle stages of limb development (e.g., paddle stage) is driven by processes operating within the limb and is likely not a result of embryo-wide constraint.

Laparoscopic-assisted colpotomy for ovariectomy in the mare.

OBJECTIVE: To describe a technique for ovariectomy through a colpotomy using a chain écraseur with laparoscopic guidance and report outcome in 4 mares. STUDY DESIGN: Case series. METHOD: After insertion of a laparoscope into the abdomen through the left flank, colpotomy was performed to allow introduction of an écraseur into the caudal aspect of the abdomen. Grasping and removal of the ovary and evaluation of the pedicle was observed via the laparoscope. The laparoscope was then inserted in the right flank for right ovariectomy. The colpotomy was closed in a continuous suture pattern using laparoscopic or long needle holders. RESULTS: Insertion of a laparoscope allowed ready identification of the ovaries and capture within an écraseur, including assurance that no other tissues were contained within écraseur chain. The mesovarial pedicles were easily be examined for hemorrhage. Surgical time for ovariectomy was 10-15 minutes with no postsurgical complications. Closure of the colpotomy healed without complications. CONCLUSION: Laparoscopic-assisted écraseur ovariectomy is inexpensive, rapid, and a safe alternative to other methods of open and laparoscopic ovariectomy.